There has been conventionally known a spring apparatus that gives electrical conductivity includes a coil spring and end coils. The coil spring has two ends and a plurality of intermediate coils canted along a centerline of the coil spring. Each of the intermediate coils has a leading portion disposed at a front angle to a normal line to the centerline and a trailing portion disposed at a back angle to the normal line. The end coils are congruent with the plurality of intermediate coils, are disposed at the two ends, have back angle means, and define a trailing portion of at least one of the end coils for locking the end coils on one end of the intermediate coils to the end coils on another end of the intermediate coils. The end coil trailing portion of the at least one of the end coils has a back angle different from the intermediate coil trailing portion back angle. The end coils are disposed at positions not interfering with deflection of the intermediate coils. Such a spring apparatus has been disclosed, for example, in Patent Document 1.
Moreover, there has been known a spring holding connector (contact) that includes a housing having a bore therethrough, a shaft rotatably and slidably arranged in the bore, an annular groove formed in one of the bore and shaft, and a circular coil spring disposed in the annular groove for slidably holding the shaft within the bore. The ends of the wire of the coil spring are welded to form a circular form. The groove is sized and shaped for controlling, in combination with a coil spring configuration, shaft mobility within the bore. Such a spring holding connector has been disclosed, for example, in Patent Document 2.    [Patent Document 1] Japanese Patent Application Laid-open No. H8-210404    [Patent Document 2] Japanese Publication of a Translation of an International Application 2006-518090